146 ODOROGRAPHIA. 



colour, and had a combined odour of thyme, lemon and geranium. 

 By fractional distillation, oil of thyme is separated into two parts : 

 the first, boiling at 178°-180" C, being a mixture of Cymene 

 Cio H^j^ and Thymene Q^^ H;^^; and the second portion boiling 

 at 230^ C, Thymol, C,o H,^ 0. 



The medicinal and powerfully antiseptic properties of Thymol 

 have enhanced the value of oil of thyme. The value of oil of 

 thyme is therefore dependent on the percentage of thymol present 

 in the sample.* 



Thymol is also abundantly contained in the essential oil of 

 the seeds of Ajowan (Ptychotis Coptica), a plant largely cultivated 

 in India. Immense quantities of this seed are sent to Germany, 

 where it is distilled. Thymol may be separated from either of 

 these essential oils (of wdiich it is the oxygenated constituent), by 

 treatment with caustic potash or soda as described below, or by 

 submitting the essential oils to a low temperature for some days. 

 When prepared by the first process, thymol occurs as an oily fluid, 

 and wdien by the second, as a crystalline solid. The following are 

 the details of the preparation of the liquid variety of thymol as 

 given by the Paris Pharmaceutical Society: — " Treat essential oil of 

 thyme with an equal volume of an aqueous solution of potash or 

 soda, and shake several times to facilitate combination. The 

 thymol dissoh^es, forming a soluble compound, whilst the thyw.cne^ 

 a hydrocarbon that accompanies it it in the oil, does not combine 

 with the alkali, and separates. Filter the solution obtained, 

 and treat with an acid, — hydrochloric acid for example — which 

 sets free the thymol. The product should be purified by w^ashing, 

 dried and distilled." 



Thymol was obtained in fine tabular crystals by Fllickiger and 

 Hanbury, who exposed the oil of ajow^an to a temperature of 0^ C. ; 

 the oil so treated yielded 35 per cent, of its weight of crystallised 

 thymol. It is stated that oil of thyme yields as much as 50 per 

 cent. 



As found in commerce, thymol consists of irregular broken 

 crystals, or thin colourless rhombic scales, nearly transparent. The 

 taste is burning and aromatic. Sp. gr., 1'028, but lighter than 

 water when fused. It is optically inactive. It melts between 50^ 



* For the efficacy of thymol in diphtheria, see Pharni. Zeit., 1890, p. 261, and 

 in chyluria, Lancet, 16th P'eb., 1891. 



